Effect of Corona Block Asymmetry on Chain Exchange in Triblock Copolymer Micelles

Chain exchange kinetics in block copolymer micelles are determined primarily by the interaction parameter (χ) and the degree of polymerization of the core block (N_core). Micelle chain conformation, determined by the block copolymer architecture, can significantly impact the kinetics. In this research, we investigated the effect of an asymmetric ABA′ architecture on chain exchange dynamics in triblock copolymer micelles. The triblock copolymer had a constant length polystyrene (PS) middle block, but different lengths of two poly(ethylene-alt-propylene) (PEP, PEP′) end blocks. Using time-resolved small-angle neutron scattering (TR-SANS), we compared the chain exchange kinetics for spherical micelles containing diblock, symmetric, and two asymmetric triblock copolymers prepared in squalane, a PEP-selective solvent. As the asymmetry parameter (r) increased, the rate of chain exchange accelerated tenfold from the diblock (r = 0) to asymmetric (0 < r < 1) and to a symmetric triblock copolymer (r = 1). Possible reasons for this behavior will be discussed.[1] Our work sheds light on the relationship between polymer architecture and micelle dynamics, thereby contributing to a better understanding for practical applications.

[1] Lodge, T. P.; Wang, E.; Zhu, J.; Bates, F. S. Solution and Bulk Structures of Asymmetric PEP-PS-PEP′ Triblock Copolymers. Macromolecules, 2023, 56 (16), 6444-6451.